1. Field of the Invention
This invention relates to a joining method of veneer sheets (hereinafter referred to as “veneers”) and joining equipment.
2. Description of the Related Art
In the conventional way to efficiently join plural short veneers without a sufficient length to be processed, on the way to carry each veneer in a perpendicular direction to the joining edges of each veneer, it is preferable to make edges of a preceding veneer and a succeeding veneer closer such that an appropriate amount of the adhesive material is supplied between the joining edges of the preceding and succeeding veneers or on one portion of one or the other side of the preceding and succeeding veneers at an appropriate time before or after the joining edges come closer. As the said adhesive materials, adhesive thread, adhesive tape or the like in which the desired adhesive materials are coated or soaked in an appropriate base material such as a string material like thread, fiber or the like, or paper tape or the like as well as other well-known materials such as thermosetting adhesive, thermoplastic adhesive or the like which are widely used.
As shown in FIG. 18 for applying the adhesive materials, if a thin type of adhesive material (an adhesive tape with holes (Sa) is used in FIG. 18) is successively applied on the top sides or the bottom sides of the veneers (T) in parallel to the carrying direction (f), this system has an advantage that for example, crack (W), over heated portion (not described in the drawings) or the like which may be involved in the veneers can be also strongly amended and joined. However, such a system has a disadvantage which is a major issue, i.e. the strength of the joining edge (Te) is not sufficient in spite of the high cost for the comparatively large amount of adhesive materials to be used. On the other hand FIG. 21 shows that if the adhesive material (adhesive tape (Sb), adhesive thread (Sc) and adhesive material (Sd) are used respectively in FIGS. 19, 20, and 21) is applied to the joining edges (Te) between the preceding veneer and succeeding veneer, or applied intensively to a small area (therein the joining edge (Te) is centrally located) including the joining edge (Te) on the top side of each veneer, shown in FIGS. 19 and 20, such a system has an advantage in which a comparatively small amount of the adhesive material enables the joining edge (Te) to be strongly joined. Therefore, it is preferable to choose one of the above joining systems of the above systems considering the feature of the single piece, cost performance, and a combination of the above system is practically utilized according to the necessity. In this connection, the reason why the adhesive material is applied to the limited small area is to cut down costs and avoid or reduce the unfavorable influence on joining process for the plywood production from the processed veneers in a certain degree while the practical strength can be obtained without actual hindrance. Although a certain clearance between the joining edges is indicated in FIG. 21 expediently to define the adhesive material (Sd), this clearance is actually unnecessary.
On the other hand, to complete the stable joining procedure quickly, it is important to apply the adhesive action immediately to the adhesive material to activate and enhance the adhesiveness. For example, pressuring action, or pressuring and heating action is provided to the adhesive materials such as pressure-sensitive adhesive material or rewet adhesive material, or heating action or pressuring and heating action is provided to the adhesive material such as the thermosetting adhesive material, furthermore, cooling action, or pressuring and cooling action is provided to the thermoplastic adhesive material respectively.
In the conventional way for applying the adhesive material between the joining edges of the preceding and succeeding veneers or applying intensively to the limited small area on the top or the back side of each veneer including the joining edges, it is possible to supply the adhesive material to the veneers accordingly while being carried on the conveyor. However, the adhesive action is usually enhanced, barring one exception where the adhesive material in which thermoplastic adhesive material is used, but adhesive enhancement is not necessarily used; while natural cooling is provided, which may not be able to carry out a proper cooling function at high temperatures, and joined single pieces can be bonded up and down, which makes it difficult to handle for example, shown in FIG. 17, by providing a joining operation position (Y) on the way of the veneer carrying conveyer, providing appropriate adhesive enhancing device (6) comprising adhesive enhancing function to at least one side of the top surface and the bottom surface of the single piece (the said joining operation position is provided on both sides in the embodiment shown in FIG. 17). Furthermore the said adhesive enhancing device (6) is provided in contact with or with a variable distance to the single pieces (T1) to (T7), and after stopping once, each joining edge (Te) between veneers at the joining operation position, work the adhesive enhancing device (6) to complete supplying adhesive enhancing action to the adhesive material (not indicated in the drawing) only in the sufficient period to activate the adhesive function, then each single piece is again carried.